Betaines of the general formula ##STR1## wherein R.sup.1 is an acyl group of a fatty acid with 8 to 18 carbon atoms,
R.sup.2 is a divalent, aliphatic hydrocarbon group with 2 to 5 carbon atoms, PA1 R.sup.3, R.sup.4 independently of one another are aliphatic hydrocarbon groups with 1 to 4 carbon atoms, and PA1 R.sup.5 is the --CH.sub.2 -- or --(CH.sub.2).sub.2 -- group, PA1 R.sup.1 is an acyl group of a fatty acid with 8 to 18 carbon atoms or a mixture of these fatty acids, PA1 R.sup.2 is a divalent aliphatic hydrocarbon group with 2 to 5 carbon atoms, PA1 R.sup.3, R.sup.4 independently of one another are aliphatic hydrocarbon groups with 1 to 4 carbon atoms, PA1 R.sup.5 is the --CH.sub.2 -- or --(CH.sub.2).sub.2 group, PA1 R.sup.6 is the acyl group of a polymer fatty acid with x acyl groups, PA1 x is a number from 2 to 5 and 95 to 70% by weight of water, alkali metal salts and optionally conventional additives such as auxiliary solvent, preservatives, etc. PA1 R.sup.1 preferably is the acyl group of a fatty acid mixture with, on the average, about 12 to 14 carbon atoms, such as the mixture of coconut oil fatty acids. PA1 R.sup.2 preferably is an alkylene group having the formula --(CH.sub.2).sub.2 -- or --(CH.sub.2).sub.3 --. PA1 R.sup.3 and R.sup.4 preferably are methyl groups. PA1 R.sup.5 preferably is the --CH.sub.2 --. PA1 R.sup.6 preferably is an acyl group of the dimer acid.
have long been known. They are described in various patents, of which the German Auslegeschrift 10 62 393 is an example.
Betaines are used as amphoteric surfactants, particularly for hair- and skin-cleaning preparations, such as shampoos, foam and shower gels gentle to the skin, feminine hygiene and skin care products. They improve the dermatological properties of anionic surfactants and cause skin to be pleasant to touch. In addition, the betaines can be used as surfactants for industrial purposes, for example, in the textile industry, or as anticorrosive agents in metal-treating liquids.
The betaines of the state of the art are distinguished by their high foaming ability, the foam being stable even in the presence of salts which are dissolved in water and cause it to be hard. As desirable as this foaming tendency may be for many applications, it does interfere with some uses, so that the availability of low foaming betaines is desirable particularly if these betaines are used for technical purposes.
The Czechoslovakian Patent 260933 disclosed betaines, the fatty acid group of which is derived from dimer and trimer fatty acids. Such polymeric fatty acids are commercially available under the name of dimer and trimer acids. The dimer acids are a mixture of dicarboxylic acids with a total of, generally, 36 carbon atoms, which are synthesized by covalently linking unsaturated fatty acids with 18 carbon atoms at temperatures above 200.degree. C., generally in the presence of clay minerals. Oleic acid, linoleic acid and linolenic acid are generally used as unsaturated fatty acids. The dimer acids, obtained in this manner, can subsequently be hydrogenated.
With regard to the synthesis and use of dimer acids and their physical and chemical properties, reference is made to the publication: "The Dimer Acids: The chemical and Physical Properties, Reactions and Applications", edited by E. C. Leonard; Humko Sheffield Chemical, 1975, Memphis, Tenn.
The dimer acid can correspond to the following formula: ##STR2##
The trimer acids are synthesized in a similar manner and are tricarboxylic acids which are obtained by the trimerization of unsaturated fatty acids and generally contain 54 carbon atoms.
These polymer acids are obtainable commercially in different degrees of purity, because the crude reaction product, resulting from the dimerization of unsaturated C.sub.18 fatty acids, contains, aside from dimer acid, trimer acid of the monomeric carboxylic acids and appreciable amounts of intermediates of unknown structure, the molecular weight of which ranges from C.sub.18 to C.sub.36. If betaines are synthesized using polymer acids, it is noted that, as the purity of the polymer acids increases, the viscosity of their aqueous solutions increases greatly at comparable concentrations until said solutions finally become gelatinous and are no longer free flowing. For example, when crude dimer and trimer acid mixtures are used, it is possible to prepare betaine solutions with a solids content of about 15 to 25% by weight. However, if purified, particularly distilled dimer acids are used, the aqueous solutions become already solid at solids contents above about 4 to 5% by weight. This limits the usability of such betaines based on dimer acid. Particularly for cosmetic applications, but also in numerous technical applications, such as the treatment of textiles, the use of rather pure substances, which are well defined, is aimed for in order to keep toxicological risks as small as possible. Therefore betaines especially based on purified polymer fatty acids are particularly important.
It is known to mix betaines, which were synthesized separately using different fatty acids, after their synthesis in order to obtain particular application properties. For example, the EP-A2 0 121 791 discloses a preparation for cosmetic formulations, which contains a mixture of coconut oil amidopropylbetaine and oleoamidopropylbetaines in the ratio of 1:4 to 3:2. This betaine mixture has thickening and foam-reinforcing properties in aqueous cosmetic preparations and shows improved emulsifying properties, for example, for jojoba oil.